Owing to the characteristics of such as power saving, lightweight and thin shape, the liquid crystal displays have recently been spread at a high rate instead of the conventional CRT displays. As a common liquid crystal displays, one comprising incident side polarizing plate 102A, an output side polarizing plate 102E and a liquid crystal cell 104 as shown in FIG. 6 can be presented. The polarizing plates 102A and 102B are provided for selectively transmitting only a linear polarization (shown schematically by the arrow in the figure) having an oscillation plane in a predetermined oscillation direction, disposed in a crossed Nicol state with their oscillation directions perpendicular with each other. Moreover, the liquid crystal cell 104 includes a large number of cells corresponding to the pixels and is disposed between the polarizing plates 102A and 102B.
As the liquid crystal displays, those of various systems have been put into practice according to the alignment form of the liquid crystal molecules comprising the liquid crystal cell. Recently, those of the VA (vertical alignment) system are the mainstream. The liquid crystal displays of the VA system are widely used mainly for the liquid crystal televisions.
As to the liquid crystal cells used for the above-mentioned liquid crystal displays of the VA system, since the liquid crystal molecules are aligned vertically, the liquid crystal cells as a whole has the optical characteristics to function as a positive C-plate. For example, if the liquid crystal cell 104 of the liquid crystal display 100 shown in FIG. 6 has such optical characteristics, a linear polarization transmitted the incident side polarizing plate 102A passes through a cell portion in the non driven state out of the liquid crystal cell 104 without the phase shift so as to be blocked by the output side polarizing plate 102B. On the other hand, at the time of passing through a cell portion in the driven state out of the liquid crystal cell 104, the linear polarization has the phase shift so that a light beam according to the phase shift amount is transmitted and outputted from the output side polarizing plate 102B. Therefore, by optionally controlling the driving voltage of the liquid crystal cell 104 per cell, a desired image can be displayed on the output side polarizing plate 102B side. The liquid crystal display 100 is not limited to those having the light transmission and shielding embodiment mentioned above. A liquid crystal display provided such that a light beam outputted from a cell portion in the non driven state out of the liquid crystal cell 104 is outputted after transmitting through the output side polarizing plate 102B and a light beam outputted from a cell portion in the driven state is shielded by the output side polarizing plate 102B is also proposed.
Considering the case with a linear polarization transmitting a cell portion in the non driven state out of the VA system liquid crystal cell 104 mentioned above, since the liquid crystal cell 104 has birefringence and has different refractive indexes between a thickness direction and an plane direction, although a light beam inputted along the normal line of the liquid crystal cell 104 out of the linear polarization transmitted the incident side polarizing plate 102A is transmitted without the phase shift, a light beam incident in the direction inclined with respect to the normal line of the liquid crystal cell 104 out of the linear polarization transmitted the incident side polarizing plate 102A becomes an elliptical polarization due to the retardation generated at the time of transmitting the liquid crystal cell 104. This phenomenon is caused because the liquid crystal molecules aligned vertically in the liquid crystal cell 104 functions as a positive C-plate. The size of the retardation generated to the light beam transmitted the liquid crystal cell 104 (transmitted light beam) is influenced also by such as the birefringence value of the liquid crystal molecules sealed inside the liquid crystal cell 104, the liquid crystal cell 104 thickness, or the wavelength of the transmitted light beam.
Due to the above-mentioned phenomenon, even in the case with a cell in the liquid crystal cell 104 is in the non driven state and a linear polarization should be transmitted as it is so as to be shielded by the output side polarizing plate 102B, a part of the light beam outputted in the direction inclined with respect to the normal line of the liquid crystal cell 104 is leaked from the output side polarizing plate 102B. Therefore, according to the conventional liquid crystal display 100 as mentioned above, a problem of the deterioration of the display quality of an image observed from the direction inclined with respect to the normal line of the liquid crystal cell 104 compared with an image observed from the front side (viewing angle dependency problem) has been present.
In order to remedy the problem of the viewing angle dependency in the conventional liquid crystal display 100 as mentioned above, a variety of techniques have been developed up to now, and a typical one thereof is a method of using an optical functional film. In the method of using the optical functional film, the problem of the viewing angle characteristics is remedied by disposing an optical functional film 60 having given optical characteristics between a liquid crystal cell 104 and a polarizing plate 102B as shown in FIG. 6. As the optical functional film used to remedy such a problem of the viewing angle characteristics, retardation films exhibiting a refractive index anisotropic property have been used, and have come to be widely used as a means for remedying the viewing angle dependency in the above-mentioned liquid crystal displays.
Heretofore, the above retardation film generally has the construction in which as shown in FIG. 7, an alignment layer 72 is provided on an arbitrary transparent substrate 71 and a retardation layer 73 having liquid crystal molecules is formed on the alignment layer 72, so that the liquid crystal molecules are aligned by an alignment controlling power of the alignment film and thereby a desired refractive index anisotropic property is exhibited. As such retardation films, as disclosed in Patent document 1 or 2, for example, there are retardation films in which a retardation layer having a molecular structure with cholesteric pattern regularity (a retardation film exhibiting birefringence) is formed on a substrate having an alignment layer. Meanwhile, Patent document 3 discloses a retardation film in which a retardation layer composed of a discoid compound (a retardation layer exhibiting birefringence) is formed on a substrate having an alignment layer.
The above retardation films are useful in that the problem of the viewing angle dependency of the liquid crystal display can be largely remedied by appropriately designing the refractive index anisotropic property to offset the retardancy caused in the liquid crystal cell of the liquid crystal display. However, since the conventional retardation film took, as an indispensable component, the alignment layer for aligning the above liquid crystal molecules, there was a problem in the adhesion property between the alignment layer and the retardation layer.
In order to solve this problem, for example, Patent document 4 proposes that the adhesion property is improved by thermally treating liquid crystals and the alignment layer. According to this method, however, when the substrate is not a glass substrate but a substrate having a low wet heat resistance (for example, TAC), it may be that the substrate is expanded or shrunk owing to the influence of moisture. Consequently, this method was hardly said to be a method sufficient for the substrate susceptible to moisture. There was also a problem that interference fringes are formed through multiple reflections between the layers owing to the existence of the alignment layer.
In order to remedy the viewing angle dependency of the liquid crystal display adopting the VA system with use of the alignment film, a method employing two retardation films: a retardation film having a function as a negative C-plate and another having a function as an A plate or B plate is generally used. As the method using such two retardation films, for example, there were used an approach as shown in FIG. 8A in which a liquid crystal cell 104 is sandwiched between a retardation film 61 having a function as the negative C-plate and a retardation film 62 having a function as the A plate, and an approach as shown in FIG. 8B in which a retardation film 61 having a function as the negative C-plate and a retardation film 62 having a function as the A plate are laminated upon an incident side polarizing plate 102A.
The approaches, in which the problem of the viewing angle dependency is remedied by using such two retardation films, is useful in that the problem of the viewing angle dependency can be remedied in liquid crystal display using liquid crystal cells having various optical characteristics, by changing the combination of the retardation films. However, there was a problem in that use of two retardation films thickened the liquid crystal displays or made a producing method complicated.
Meanwhile, as mentioned above, the configuration shown in FIG. 7 is general as the above retardation films. However, the retardation film having such a configuration is useful in that the liquid crystal molecules are likely to be aligned easily owing to the use of the alignment layer, but there was a problem in the adhesion property between the alignment layer and the retardation layer.
To cope with such a problem, the present inventors developed, as a retardation film capable of exhibiting desired optical characteristics without using an alignment film, a retardation film comprising: a substrate, and an optical functional layer which is directly formed on the substrate and has a rodlike compound aligned randomly and homogeneously. Such a retardation film having no alignment film is useful in that the film has excellent adhesion property between the optical functional layer and the substrate and that the optical functional layer having the rodlike compound aligned in the random-homogenous manner mentioned above excellently exhibits the optical characteristics as the negative C-plate. Accordingly, such a retardation film have attracted attention as having the quality exceeding those of the conventional retardation films in terms of the durability and stability in the optical characteristics.
However, the above-mentioned retardation film having no alignment film is formed by coating a composition for forming an optical functional layer containing the above rodlike compound onto the substrate having the property as the negative C-plate. In some cases, it is difficult to form the random-homogenous alignment having a uniform quality with the composition for forming an optical functional layer conventionally used. There was also a problem that the optical functional layer became clouded.                Patent Document 1: Japanese Patent Laid-Open (JP-A) No. H03-67219        Patent Document 2: JP-A No. H04-322223        Patent Document 3: JP-A No. H10-312166        Patent Document 4: JP-A No. 2003-207644        